Electronic devices such as mobile phones are becoming increasingly complex. The options available for user selection and the functions the devices perform all put a strain on the man-machine interface that needs to be intuitive and simple to use. One desirable requirement particularly for communications devices is to restrict the number of keys. One consequence of this is that an individual key may initiate several functions.
Another requirement for portable electronic devices is that they are small and easy to carry. This puts an additional constraint on the keys as they must also be relatively small.